1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to an apparatus and method for performing uplink synchronization in a wireless communication system.
2. Discussion of the Background
In a common wireless communication system, although an uplink bandwidth and a downlink bandwidth are different, only one carrier is chiefly taken into consideration. Even in 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), the number of carriers forming uplink and downlink is 1, and an uplink bandwidth and a downlink bandwidth are commonly symmetrical to each other on the basis of a single carrier. A multiple carrier system is recently introduced.
A multiple carrier system means a wireless communication system capable of supporting a carrier aggregation (CA). The carrier aggregation is technology for efficiently using fragmented and small bands, and it has an effect that a logically large band is used by binding a plurality of bands which are physically non-contiguous to each other in the frequency region.
In order for a mobile station to access a network, the mobile station must perform a random access procedure. The random access procedure may be divided into a contention-based random access procedure and a non-contention-based random access procedure. The greatest difference between the contention-based random access procedure and the non-contention-based random access procedure lies in whether a random access preamble is dedicated and designated to one mobile station. In the non-contention-based random access procedure, contention (or a collision) between mobile stations does not occur because a mobile station uses a random access preamble dedicated thereto itself. Here, the term ‘contention’ means that two or more mobile stations attempt a random access procedure using the same random access preamble through the same resources. In the contention-based random access procedure, there is a possibility of contention because a mobile station uses a randomly selected random access preamble.
Objects of a mobile station to perform a random access procedure for a network may include initial access, handover, a scheduling request, timing alignment, and so on.
A UE has performed a random access using one carrier in a conventional single carrier system. But with regards to current CA support, the UE is able to support the random access with multiple component carriers. There is a need for the detailed random access procedure of a UE in multiple component carrier system.